Validation of a Chimera RANS Method for Transient Flows Induced by a Full-Scale Berthing Ship

H.-C.Chen (Texas A&M University, USA)

E.Huang (Naval Facilities Engineering Service Center, USA)

ABSTRACT

A chimera Reynolds-Averaged Navier-Stokes (RANS) method has been developed for time-domain simulation of transient flow induced by a ship approaching a berthing structure. The method solves the mean flow and turbulence quantities on embedded, overlapped, or matched multiblock grids. The unsteady RANS equations were formulated in an earth-fixed reference frame and transformed into general curvilinear, moving coordinate systems. A chimera domain decomposition technique has been employed to accommodate the relative motions between different grid blocks. Calculations have been performed for a 1/8-scale model barge and a full-scale motor vessel in berthing operations. Comparisons have been made between the computations and measurements to demonstrate the feasibility of the chimera RANS approach for time-domain simulation of the hydrodynamic coupling between the ship and berthing structures. The numerical solutions successfully captured many important features of the transient flow around a berthing ship including the underkeel flow acceleration, wake flow separation, and water cushion between the ship and harbor quay wall.

INTRODUCTION

Berthing damage can result in substantial economic and operational penalties. Even in a well executed berthing, a large ship possesses enormous kinetic energy that could seriously damage the berthing structure as well as the ship itself. Fender systems are provided at a berth to absorb the kinetic energy of the berthing ship and to mitigate impact forces. In order to improve the design of berthing facilities, it is desirable to develop a reliable hydrodynamic assessment system for accurate time-domain simulation of the berthing processes which involve complex interactions among the ship, the fender system, and arbitrary harbor floor bathymetry. Recently, Chen, Chen and Davis [1], Chen, Chen and Huang [2] Chen, Chen, Davis and Huang [3], and Chen and Chen [4] developed a chimera RANS method for the simulation of transient flows induced by berthing operations of practical ships in fully sheltered harbors. The method solves the mean flow and turbulence quantities on embedded or overlapped grids using a domain decomposition approach. Calculations have been performed for a DDG-51 ship in combined translational and rotational motions to demonstrate the capability of the chimera RANS method for time-domain simulation of berthing ships. The numerical solutions successfully captured many important features of transient flow around a berthing ship including the underkeel flow acceleration, wake flow separation, water cushion between the ship and harbor quay wall, and the complex interactions between the bow, shoulder, and stern waves. A direct validation of the accuracy of these simulation results, however, was not possible due to the lack of experimental data.

In order to verify the accuracy of the chimera RANS method for berthing simulations, model experiments have been conducted recently by Huang, Davis, Kim and Chen [5], [6] in a shallow water basin using a 4.572 m (15 ft) barge model. Current meters and wave gages were used to measure the fluid velocities and wave elevations at selected locations along the path of the berthing barge. Time-domain simulations have been performed for the berthing barge at various approaching speeds and water depths to evaluate the accuracy and overall capability of the chimera RANS method.



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